Method of purifying silver iodide



Patented Apr. 16, 1935 rarest m-er I Charles. wrGirvin, Long Beach, Calif assignor to Deepwater Chemical v 0., Ltd, Los Angeles, Calif., a corporation of Galifornia No Drawing.

Application October 26,1933, Serial.No. 695,331

' This invention relatesto methods of purifying water-insoluble metal iodides, such as silver is obtained in the treatment of oil field waste waters, brines, etc. with a silver salt according to the method of recoveringiodine therefrom as described inU. S. Patent No. 1,837,777. 'Such silver iodide precipitate may be more or less contaminated by othersilver halidesand also with organic impurities contained in the waste water or brine which are absorbed by the precipitate.

I It is an-object of the present invention to provide a simple and practical method of purifying such silver iodide so as to enable the subsequent preparation therefrom of pure iodine or commercial iodine compounds.

The crude silver iodide precipitate recovered as aforesaid contains small amounts of silver bromide and silver chloride, as Well as iron hydroxidadirt, organic matter, etc. The presence of organic matter is often a source of especial difliculty in the purification methods as heretofore employed. Some oi'the organic matter may be volatilized'or carbonized by heating the crude silver iodide, but it cannot always be completely removed in this way. 7 r p According to the invention, the crude silver iodide, preferably after being heated to remove or-carbonize as much organic matter as possible, is dissolved in a strong aqueous solution of a water-soluble metal iodide, for instance an alkali metal iodide such as potassium iodide or sodium iodide. The strong iodide solution reacts with the silver bromide and silver chloride in the crude material to convert the said halides to silver iodide and the corresponding soluble chloride or bromide, according to the following typical equation:

AgBr+KI=Agl+KBr used for the preparation of iodine or commercial iodine compounds, according to well known" methods. v I

- In'ac'tual practice the methodof the invention has been employed to prepare potassium'iodide; for instance, from crude silver iodide recovered 5;. from oil field' brines or Waste waters. Thecrudesilver iodide is first subjected to a sufficiently high temperature to volatilize or carbonize organic matter contained in it. It is thentreated with a suilicient excess of a nearly saturated-aqueous potassium iodide solution to dissolve all of' thesilver iodide and other accompanying: silver halides, whereby such halides are converted? to silver iodide with formation of the corresponding potassium halides. The solution of: silver and potassium halides is filtered from insoluble matter, and the clearfiltrate isdiluted with sev era l times its volume of water so as to-reprecipi tate silver iodide, while the water-solublepota'ssiun'i halides remain in solution. The repreoi'pitated silver iodide is filtered out and-washed; being thusseparated in a high degree of purity Potassium iodide may then beprepared from the pure silver iodide in any known manner; for example, by redissolving inpotassiumiodide solution, precipitating the silver by reduction with a metal such as zincto leave zihciodide in solution, adding potassiumcarbonate to such solution to precipitate zinc carbonate filtering off? thelatter, leaving a substantially pure solutiori- 3g; of potassium iodide, from which the-salt may;

' be crystallized.

By similar procedure the crude silver iodide may be dissolved in a strong solution of any suitable iodide which will convert thesilver chloride and bromide present to water-insoluble silver iodide and a water-soluble chloride and bromide, the solution being filtered from insoluble matter, then diluted to repre-cipitate silver iodide, which is separated from the solutionof 40 water-soluble salts. Specifically, a solution of sodium iodide or other alkali metal iodide, in-' stead of potassium iodide, may be utilized for dissolving thecrude silver iodide.

It will be apparent also that a similar method of purification may be employed for other Waterinsoluble metal iodides, such as mercurous iodide Cal 1. The method of purifying crude silver iodide which is contaminated with other silver halides, which comprises dissolving the contaminated crude product in a concentrated aqueous solution of potassium iodide, diluting the solution so as to precipitate silver iodide, and separating the silver iodide.

2. The method of purifying crude silver iodide which is contaminated with other silver halides, which comprises dissolving the contaminated crude product in a concentrated aqueous solution of potassium iodide so as to convert the contaminating silver halides to silver iodide and potassium salts of said contaminating halides, diluting the solution was to precipitate silver iodide while retaining the potassium halides in solution; and separating the silver iodide.

3. The method of purifying crude silver iodide, which comprises dissolving it in a concentrated aqueous solution of potassium iodide, filtering out insoluble impurities, diluting the solution so as to precipitate silver iodide, and separating the silver iodide from the solution.

4. They method of purifying crude silver iodide, which comprises heating it so as to separate organic impurities, dissolving it in a concentrated aqueous solution of potassium iodide, filtering out insoluble impurities, diluting the solution so as to precipitatesilver iodide, and filtering the silver iodide from the solution.

5. The method of purifying crude silver iodide which is contaminated with other silver halides, which comprises dissolving the crude product in a concentrated aqueous solution of a waters olubl e metal iodide which will decompose the contaminating silver halides and convert the same to silver iodide and water-soluble halides of the metal of said water-soluble iodide, diluting the solution to reprecipitate silver iodide, and separating the precipitated silver iodide from the aqueous solution.

6. The method of purifying crude silver iodide, which comprises dissolving the crude product in a concentrated aqueous alkali-metal iodide solution, dilutingthe solution to reprecipitate silver iodide, and separating the precipitated silver iodide from the aqueous solution. 7

'7. The method of purifying crude silver iodide, which comprises dissolving the crude product in a concentrated alkali-metal iodide solution, separating insoluble impurities, diluting the solution to reprecipitate silver iodide, and separating the precipitated silver iodide from the aqueous solution.

8. The methodof purifying crude silver iodide which comprises dissolving the crude product in a'concentrated sodium iodide solution, diluting the solution to reprecipitate silver iodide, and separating the precipitated silver iodide from the aqueous solution.

9. The method of purifying crude silver iodide which comprises dissolving the crude product in a concentrated sodium iodide solution, separating insoluble impurities, diluting the solution to reprecipitate silver iodide, and separating the precipitated silver iodide from the aqueous solution.

10. The method of purifying a crude waterinsoluble metal iodide which is contaminated with other water-insoluble halides, which comprises dissolving the crude product in a concentrated solution of a water-soluble iodide which will convert the contaminating halides to the water-insoluble metal iodide and water-soluble salts of the halides, diluting the solution so as to reprecipitate the water-insoluble metal iodide, and recovering the precipitate.

11. The method of purifying a crude waterinsoluble metal iodide which is contaminated with other water-insoluble halides, which comprises dissolving the crude product in a concentrated solution of an alkali-metal iodide, diluting the solution so as to reprecipitate the'waterinsoluble metal iodide, and recovering the precipitate.

12. The method of purifying a crude Waterinsoluble metal iodide which is contaminated with other water-insoluble halides, which comprises dissolving the crude product in a concentrated solution of potassium iodide, diluting the solution so as to reprecipitate the water-insoluble metal iodide, and recovering the precipitate.

CHARLES W. GIRVIN. 

